|The rare example of a heroic schemer.|
In USR, we can simply call "manipulative" a Specialism. Ego rolls are used for social combat, though a particularly oblivious character might use Wits to try and puzzle out what their more clever opponent is trying to say.
In Microlite 20, it's a MIND + Communication roll. The Performance class ability (page 19 of the Fantasy Expansion) is based on the D&D Bard ability, but a schemer character can use it, especially if it's limited to the Fascinate (distracting the target with words that discourage -- or arouse -- them) or Inspire Courage (a schemer is a master at giving a rousing speech) effects. The Connections class ability (page 18) is common, too.
Putting a long-term plan into play in a single game session would take a lot of set up. While planning a scheme can be fun in itself, the end results of one -- getting your opponent to give in without drawing your sword or using a spell -- can be simulated a lot more easily than it first appears.